Just came back to check here, and I do think that there is some to search through in GEMA. I'm not certain how far we can get through that, but I can, in fact, confirm what was mentioned by Lord Thames - there's a good variety under Spectrum Music, with names familiar to us, such as Bennett, Ludlow, and Dickinson.
And with regards to other leads... MCT did release some CD compilations, of which they were entirely unique and were NOT released on Vinyl. Some things could be of interest, therein. While I agree that Ludlow has the potential to be a lead, I do have a feeling that MCT could also have some tracks on their CD collections, which were used in LGFG.
I personally say there's a chance for something to be on MCT albums, or CDM Music (The composer for "Sunrise Canyon", which, as has been stated, was actually "San Diego", Dominique Guiot, had new tracks on both of those labels. It's the matter of that being the only "modern wave" track which entices me to believe MCT or CDM has some of the missing tracks from LGFG1). But I will also watch the search on GEMA with interest, in case that turns something up.
And re: Bruton? Given their sound in the 80s, I don't personally believe that they have anything of value, but I could also take a look through BRD, BRF-BRH, BRR, BRS. The reason I mention those prefixes in particular is the fact that I believe that, if Bruton DOES contribute any tracks to LGFG, they would be there.